Even if you assume their wealth is stolen and they do nothing for job creation etc., there is no reason to assume that their gains are correlated with anyone else’s losses.
To be a utility monster, you have to say that the suffering they cause is still a net win specifically because of their pleasure.
I suppose you could say it about budget airlines who nickel-and-dime you for everything and take you to an airport that is “near” your destination in the way that Dublin is “near” Belfast — lots of small irritations causing a small number of people to be very happy.
If you pick a random person on the street and gave them a million dollars, it would be life changing. Paying off all debt, move to a new location, buy a house, set up investments to ensure that food and the mortgage are paid in perpetuity. If you give a million dollars to a billionaire, it is a rounding error on their total assets, and does not substantively change their lifestyle. Conversely, taking a million dollars, or even nine hundred million dollars, from a billionaire, will not significantly affect their lifestyle, and that amount could improve the lives of many others. This is one reason why taxation is ethical from a utilitarian perspective.
But they're often equipped to construct a much more valuable experience from an identical marginal wealth increase.